Q345NH is a Chinese standard GB/T 4171 weathering steel with medium strength and good atmospheric corrosion resistance. Its main differences from other common weathering steels lie in strength grade, chemical composition, corrosion resistance, toughness, and applicable scenarios.
1. Compared with Q235NH (lower‑strength weathering steel)
Strength:Q345NH has higher yield strength (≥345 MPa) vs Q235NH (≥235 MPa).
Structural performance:Q345NH can bear greater loads; Q235NH only for light, non‑load‑bearing parts.
Corrosion resistance: Similar in rural/urban atmosphere; Q345NH slightly better in industrial environment due to finer microstructure.
Application: Q235NH for fences, light brackets; Q345NH for main structures.
2. Compared with Q355NH (higher‑strength Chinese weathering steel)
Strength level:Q355NH (≥355 MPa) is slightly stronger than Q345NH.
Cost & weldability:Q345NH cheaper, better weldability and cold formability.
Corrosion performance: Almost identical; both form similar stable patina.
Usage: Q345NH for general engineering; Q355NH for heavy‑load bridges, large machinery.
3. Compared with 09CuPCrNi‑A (traditional Chinese weathering steel)
Composition:09CuPCrNi‑A relies more on phosphorus (P) for corrosion resistance; Q345NH uses a more balanced alloy system (Cu, Cr, Ni, low P).
Low‑temperature toughness:Q345NH significantly better; 09CuPCrNi‑A more brittle at low temperatures.
Weldability: Q345NH superior; 09CuPCrNi‑A prone to embrittlement in welding.
Corrosion: Similar in dry atmosphere; Q345NH more stable in humid/acid environments.
4. Compared with S355J0WP (European EN weathering steel)
Standard: Chinese GB vs European EN.
Strength: S355J0WP (≈355 MPa) ≈ Q355NH, higher than Q345NH.
Low‑temperature impact toughness:S355J0WP designed for guaranteed impact at 0 °C; Q345NH not strictly certified for cold regions.
Corrosion: Comparable atmospheric resistance; S355J0WP slightly better in coastal industrial zones.
5. Compared with Corten A / Corten B (US ASTM weathering steel)
Corten A (A242): Similar strength to Q345NH, but higher P content → poorer toughness.
Corten B (A588): Higher strength (≈415–450 MPa) than Q345NH, closer to Q460NH.
Corrosion: Corten series slightly better in severe industrial environments; Q345NH more cost‑effective for general use.
Supply: Q345NH widely available and cheaper in China; Corten more common in international projects.
6. Compared with high‑strength weathering steels (Q460NH, Q550NH)
Strength gap is obvious: Q460NH/Q550NH have much higher yield strength.
Toughness & weldability: Q345NH much easier to process, less preheating needed.
Application: Q345NH for conventional outdoor structures; Q460NH+ for heavy machinery, large bridges, high‑rise structures.
